Globoid cell leukodystrophy (GLD) is a progressive disorder of the nervous system which is the consequence of a deficiency of galactosylceramide beta-galactosidase. The disease occurs in both dogs and humans although there are subtle enzymatic differences between the species in terms of vaious beta-galactosidase activities. This investigation will develop optimum assay conditions and characterize the enzyme kinetics and stability of 4-methylumelliferyl, GM1 ganglioside, lactosylceramide, and galactosylceramide beta-galactosidases in serum, leukocytes, and cultured fibroblasts from dogs and humans. The effects of various tissue culture conditions on these B-galactosidase activities in canine and human fibroblasts will be evaluated. The optimized assays will be applied to dogs or individuals who are either carriers or affected with GLD. Various enzyme fractionation procedures, especially isoelectric focusing, will be utilized in the study of serum, leukocytes, and fibroblasts in canine and human GLD. Procedures for cell hybridization of cultured canine and human fibroblasts and selection of hybrid cells will be developed. Various genetic crosses will be made utilizing fibroblasts from humans and dogs with GLD. Fractionation of beta-galactosidase activities in the human-dog hybrid cells will be studied by isoelectric focusing and the results compared to those of the parental cell lines. Other lysosomal enzymes will also be screened by electrophoretic and electrofocusing techniques in both the hybrid and canine fibroblasts. Cytogenetic analysis of the hybrid cells will be performed and attempts will be made to localize the genetic control of various beta-galactosidase activities to specific chromosomes in both species.